1. Field
Example embodiments relate to an organic thin film transistor (OTFT) including a phosphate-based self-assembled monolayer and a method of manufacturing the same. Other example embodiments relate to an OTFT, which may include a single bond type phosphate-based self-assembled monolayer without intermolecular crosslinking, between source/drain electrodes and an organic semiconductor layer, thus exhibiting improved electrical properties, e.g., increased charge mobility, and to a method of manufacturing the same.
2. Description of the Related Art
After the development of polyacetylene, which is a conjugated organic polymer having semiconductor properties, organic semiconductors are receiving attention as a novel electrical and electronic material thanks to the advantages of organic material, for example, various synthesis methods, easier formability into fibers or films, flexibility, conductivity, and decreased preparation costs, and thus has been intensively and extensively studied in the wide field of functional electronic devices and optical devices.
Among devices using such a conductive polymer, research into OTFTs including a semiconductor layer formed of organic material is being conducted all over the world. Compared to conventional silicon thin film transistors, OTFTs may be advantageous because a semiconductor layer may be formed through an atmospheric pressure printing process in place of plasma-enhanced chemical vapor deposition (PECVD), and all of the fabrication processes may be carried out using a roll-to-roll process on a plastic substrate, if necessary, thus decreasing the cost of fabricating the transistor. Accordingly, the OTFT may be variously applicable to devices for driving active displays, smart cards and/or plastic chips for inventory tags.
However, the OTFT may have lower charge mobility and higher operating voltage and threshold voltage than conventional silicon thin film transistors. For example, where an OTFT having a bottom contact structure or a top gate structure, adhesion between material for source/drain electrodes and organic semiconductor material for a semiconductor layer may be undesirable due to the different surface properties thereof, and also the electrode material may have a lower work function than the organic semiconductor material, thereby forming a Schottky barrier between the semiconductor layer and the source/drain electrodes, resulting in a lower charge mobility.
In order to solve the problems, methods of surface treating the interface of the semiconductor layer and the source/drain electrodes with a self-assembled monolayer (SAM) compound have been employed. As such, the conventional SAM compound may be known to be phosphates, silanes, or thiols. Among these compounds, a phosphate-based SAM compound may be known to be a material having a dichlorophosphate functional group. Although the dichlorophosphate functional group is advantageous because it may have higher reactivity and thus may easily form the SAM on a substrate, it may be very sensitive to moisture and may be easily deformed, undesirably lowering stability.
Therefore, recently, research has been directed to the development of a novel and more stable SAM for use in surface treatment of source/drain electrodes.